Last of the summer pollen.
It looks like your White Balance is off. Otherwise, great images with the D90, Tammy and TC.
fwiw... I use the Auto WB option on my D300 and D90 bodies. However, this must be calibrated form time-to-time. fwiw, I use APS in Chicago for servicing my Nikon gear in most situations.
Also, I would suggest that you invest in a WhiBal pocket card. Then include a shot of the card when starting the shoot and when the light changes (CP filter). Then you can use the White Balance tool to sample the gray area of the WhiBal shot and then apply it to the coresspponding images. All this is assuming that you are shooting RAW (NEF) images.
Lots of asters blooming now - many "visitors". Still many good photo ops. As the day cools, keep an eye out for "resting" carpender bees.
Hope this helps and keep up the good shooting.